Wearable devices such as Google glass and smartwatches are gradually accepted by people, and these electronic smart devices will make people's life more and more convenient.
Conventional myopia glasses or hyperopia glasses add a concave lens or a convex lens with a fixed focal length before the eye of a person that suffers from a refractive error to correct various refractive error problems of different causes. However, conventional glasses have the troubles of optometry and lens fitting, and can only solve problems such as correction within a certain distance range. For an object beyond a certain distance, a user may be unable to obtain a clear image and has an indistinct vision, or sees the object with a difficulty that the eyes get tired easily.
Based on the foregoing case, multi-focus glasses with each lens having a plurality of different focal lengths appear. By using an example in which glasses are worn for eyes with both presbyopia and myopia, the upper portion of the glass is a myopia lens and is used to help a user to see an object at a far place clearly; the lower portion of the glass is a hyperopia lens and is used to help a user to see an object at a near place clearly. However, the user needs to see a far place through the upper portion of the glass while see a near place through the lower portion; for example, the user needs to lower the head to see an object that is low at a far place and raise the head to see a object that is high at a near place; or the user needs to manually adjust the position of the glasses, which makes the use troublesome.
Similarly, healthy human eyes and an imaging recording apparatus such as a camera or a video recorder also cannot obtain clear images of objects at all distances within a visual field. For example, when healthy human eyes see an object very close to the eyes, the eyes may also see the object unclearly or get tired.
When a plurality of different objects of different depths exists in a visual field, the lens cannot switch rapidly among different focal lengths.